Sandwich structure



April 24, 1962 H. H. HOADLEY SANDWICH STRUCTURE Filed July 3, 1959 a m 6m /M f.

INVENTOR HE NR) H. HOADLEY L Pu;

A T TORNEY United States Patent Oflice 3,931,046 Patented Apr. 24;, 1962 i STRUGTURE Henry H. 'Hoadley, South Glastonbury, Conn., assignor toUnitedAircraft Corporation, East Hartford, Conn,

a corporation of Delaware Filed July 3, 1959, Ser. No. 824,833

11 Claims' (Cl. 18934) This invention relates to sandwich structure and more particularly to high temperature structures having int nal d m in mean It is an object of this invention to provide .a sandwich structure which is capable of resisting .high temperatures as might be encountered in high speed flight 9? t t ai teasi e Wh le poss s g high damping q ities.

It is a further object of this invention to provide a sandwich structure material which comprises outer layers of heat-resistant material such as metal sheets with a filler comprising a plurality of metal spheres which are bonded together and with each of the spheres containing a substantially free mass to provide internal damping.

It is a further object of this invention to provide a method of making the internally damped metal spheres and the final sandwich structure.

These and other objects will become readily apparent from the following detailed description of the drawings in which:

FIGS. 1 through 3 illustrate the three stages of manufacturing the damped spheres of this invention;

FIG. 4 is a partial cross section of a sandwich structure showing the arrangement of the outer sheets and the metal spheres therebetween; and

FIG. 5 is a schematic illustration of a compressor blade and mechanism for plating spherical core members while they are in position in the blade.

FIG. 1 illustrates a typical spherical core which may be blown like a bubble into the spherical shape by any suitable means. If desired, the core may be mechanically formed. However, the core material is especially selected such that when exposed to elevated temperatures will melt or be reduced to a globule. The core material may be wax but preferably would be of a material having the property whereby it will soften in the range between 300 F. and 500'? F. A lightweight metal may be used, but preferably a plastic material may be used and selected from the group comprising:

Arcylate and methacrylate (Lucite) Cellulose acetate Ethyl cellulose Copolyvinyl chloride-acetate (Vinylite) The hollow spherical core 10 may be coated, if necessary, with a film of conductive material so that a thin outer shell may be electroplated thereon. Thus a thin outer shell 12 as seen in FIG. 2 then surrounds the core 10 to form a strong spherical body which is resistant to high temperatures. The outer coating 12 may be such high temperature metal as nickel, iron or their alloys as disclosed in copending patent application Serial No. 818,061, filed June 4, 1959, for Lightweight Porous Structures and Methods of Making Same, by Morris W. Mote, Roland B. Fischer, Glenn R. Schaer and Benjamin C. Allen.

Subsequent to the electroplating of outer shell 12, the sphere may be subject to a relatively high temperature which is above the softening or melting point of inner core 10 such that it is reduced to a relatively small loose globule such as 14 shown in FIG. 3. Incidentally, the core material should have the characteristic of having a low adhesive quality with respect to the outer shell so that once the core material has been reduced to a small 2 mass it will remain relatively loose within the outer shell 12.

The mass 14 may not assume a perfectly spherical shape as shown by example in FIG. 3 but instead in its soft state will assume a fairly rounded shape depending on the surface tension of the material. Further, at operating temperatures of the final structure, the corematerial may remain in a liquid state.

As shown in'FIG. 4, the spheres16- may be placed between outer metal plate-like surfaces 18 and 20 and bonded to each other as well as ,tothe plates 18 and 20. The spheres may be coated with a brazing material before being placed in the form of the final sandwich structure and the entire assembly heated orrsuitably cured so as to cause the spheres 16 to be bonded to each other and the entire mass of spheres simultaneously bonded to the plates 18 and 20.

FIG. 5 is a schematic illustration of one means for making damped compressor blades of lightweight construction but resistant to high temperatures. Thus, for examp e, a compressor blade 22 may be provided as a hollow airfoil member. Blade 22 may be formed in one piece or of a curved sheet metal. The completed spherical cores may be placed within the hollow portion 24 of the blade to completely fill the center thereof. A plating solution can be pumped through the hollow blade by a suitable pump 26 so that the cores will each acquire a coating of metal. In this manner, the plating material itself may form the bond between the balls and between the balls and the inside walls of the compressor blade. The entire structure is then heated to a desired temperature so that the core material will be reduced to a small free mass within each of thehollow metal spheres to provide suitable internal damping.

As a result of this invention high strength sandwich structures are provided which can resist high temperatures and are provided with adequate internal damping as, for example, in compressor blading with even a small amount of internal damping, a very effective means is provided for reducing oscillatory stress during operation of the compressor.

Although one embodiment of this invention has been illustrated and described herein, it will be apparent that various changes may be made in the construction and arrangement of the various parts without departingfrom the scope of the novel concept.

I claim: 1

1. A sandwich composite structure including plate-like outer layers of substantially heat-resistant material, an intermediate layer between said outer layers and bonded to said outer layers, said intermediate layer comprising a plurality of hollow spheres bonded together, and each of said spheres having within its hollow a substantially loose relatively small mass.

2. A sandwich composite structure including plate-like outer layers of substantially strong formable material, an intermediate layer between said outer layers and bonded to said outer layers, said intermediate layer comprising a plurality of hollow metal spheres bonded together with heat-cured material, and each of said spheres having within its hollow a relatively small substantially loose mass.

3. A sandwich composite structure includingplate-like outer layers of substantially heat-resistant metal, an intermediate layer between said outer layers and bonded to said outer layers, said intermediate layer comprising a plurality of hollow metal spheres bonded together, and each of said spheres having within its hollow a relatively small substantially loose mass.

4. In a hollow body adapted for bonding to similar bodies in the construction of rigid structures, a hollow core material, and a metal coating for said core, said core material having a softening temperature below that of said coating and having a low adhesive characteristic with respect to the metal coating whereby said core material is reduced to a relatively free globule upon heating of the body.

5. A damped body comprising a plurality of hollow spheres bonded together, each of said spheres containing a relatively movable mass.

said mass is relatively small as compared with the volume of its sphere.

9. In a sandwich-type rigid structure having plate-like outer layers of formable material, a hollow body adapted for bonding to similar bodies in the construction of said structure and for location as an intermediate layer bej tween said layers, said hollow body including a hollow core material, and a metal coating for said core, said core material having a softening temperature below that of said coating and having a low adhesive characteristic with respect to the metal coating whereby said core material is reduced to a relatively free .globule upon heating of the body.

10. In a structure according to claim 9 wherein said softening temperature is below that of said'layers.

11. In a structure according to claim 10 wherein the intermediate layer is bonded to said outer layers.

References Cited in the file of this patent UNITED STATES PATENTS 511,472 Sumovski Dec. 26, 1893 948,541 Coleman Feb. 8, 1910 1,978,494 Junkers Oct. 30, 1934 2,714,161 Featherstun July 26, 1955 2,745,173 Janos May 15, 1956 2,752,672 Tolman July 3, 1956 2,806,509 Bozzacco et al Sept. 17, 1957 

1. A SANDWICH COMPOSITE STRUCTURE INCLUDING PLATE-LIKE OUTER LAYERS OF SUBSTANTIALLY HEAT-RESISTANT MATERIAL, AN INTERMEDIATE LAYER BETWEEN SAID OUTER LAYERS AND BONDED TO SAID OUTER LAYERS, SAID INTERMEDIATE LAYER COMPRISING A PLURALITY OF HOLLOW SPHERES BONDED TOGETHER, AND EACH OF SAID SPHERES HAVING WITHIN ITS HOLLOW A SUBSTANTIALLY LOOSE RELATIVELY SMALL MASS. 